Thursday, September 1, 2016

quantum satellite

China made a splash on the scientific front recently by
launching a “quantum satellite,” a 600 kilogram laboratory of quantum optics
experiments. China has propelled itself to the forefront of quantum
communications, hack-proof schemes that rely on the no-cloning theorem of quantum mechanics to communicate over large distances. With
the satellite, they hope to establish a quantum channel between Beijing and
Vienna (China is collaborating with the Austrian Academy of Sciences), far extending the
current record of around 300 kilometers. Entangled pairs of photons will be generated
via nonlinear crystal onboard the satellite and then fired towards Beijing and
Vienna, along with some classical information on how to interpret the
measurements (the requirement it be classical, i.e. no faster than the speed
of light, prevents quantum nonlocality from violating Einstein’s special theory
of relativity). From there, the standard experiments will be performed: Bell
(or CHSH) tests to prove quantum entanglement over the 1200 kilometer distance
by looking at statistical correlations that imply the state of one photon in
Beijing depends on the other measured in Vienna, teleportation of a quantum
state, and quantum key distribution by which private keys for encryption are
shared publicly between two parties. [Full disclosure: Le’Veon Bell’s Joint Measurement is the name of a fantasy football team managed by yours truly].

The 600 kilogram satellite itself [Cai Yang/Xinhua via ZUMA Wire]

The trick behind quantum encryption is that it relies on the
property that measurement inherently destroys a quantum state. If an eavesdropper
were to intercept some communication it would be immediately obvious that they
had done so. This is in contrast to current encryption methods that are based
on the supposed difficulty of mathematical problems such as calculating the factors of large numbers
into primes (RSA, the universal method by which internet transactions take
place), elliptic curves and discrete logarithms, being some other popular examples. RSA, by the way, is vulnerable
to Shor’s algorithm, which could run on a quantum computer in the future.
China’s foray into quantum encryption seems mainly to stem from, ahem,
successful United States cyberespionage efforts penetrating Chinese networks. Successfully opening quantum channels between cities would secure
communications (though it would not aid in their own cyber subterfuge).

Other groups getting into this quantum satellite business are universities from Italy, Canada, and a Singapore/British collaboration. What about these United States, you ask? Well it seems the US government canned funding for optical quantum information processing in 2010, purportedly because its application to quantum computing was overhyped. US funding for quantum computing is quite high at $200 million per year, although it largely neglects the communications and cryptology (well, at least publicly) aspects of quantum information. However, now that quantum information science is making it to the level of White House briefings, that may be changing.